, amplitudes are never affected by the strength of stimulus. The strength of a stimulus is represented by

All voltage-gated channels closed. For Neurons, equals approximately -65mv to -70mv).

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Action Potential Stage 2. Threshold:

Membrane voltage (potential) at which “activation gates” of “voltage-gated Na+ channels” open (approximately -55 mv). Triggered, at proximal end of axon by summation of EPSPs, and spontaneously propagated down axon by entry of sodium through preceding voltage-gated Na+ channels.

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Action Potential Stage 3. Depolarization phase:

Sodium floods into the axon. Interior of axon becomes so positive that membrane potential goes to +40mv.

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Voltage-gated Na+ channels have 2 gates:

a)Activation gates whichopen at threshold, to start “depolarization phase.”b)Inactivation gates which close at beginning of “repolarization phase.”

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Action Potential Stage 4. Repolarizing phase:

Inactivation gates of voltage-gated Na+ channels close, and voltage-gated K+ channels open, allowing K+ to flood out of axon.Note: Voltage-gated K+ channels have only one gate.

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Action Potential Stage 5. Undershoot phase:

Membrane potential temporarily more negative than resting state. Since voltage-gated K+ channels are slow to close.

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Action Potential Stage 6. Sodium/Potassium Pumps

re-establish the original ion distribution, so that a subsequent action potential can occur.

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Graded Potentials (EPSPs and IPSPs) only happen at

chemical synapses

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graded potentials occur at

synapses on dendrites and neuronal cell bodies.

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Acetylcholine =

It is the most abundant neurotransmitter in the body, but is less than 5% of the neurotransmitters in the brain.

It is released by all motor neurons that activate our skeletal/voluntary muscles.

It is also released by all preganglionic autonomic neurons (parasympathetic and sympathetic), as well as post-ganglionic parasympathetic neurons.

It is the second most important neurotransmitter for learning and memory.

Excitatory in brain;

inhibitory on heart.

In brain, produces depolarization and

EPSPs by opening

ligand-gated sodium (Na+) channels.

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Glutamate =

It is the most abundant excitatory neurotransmitter in the brain, and accounts for approx. 35% of all neurotransmitters in the brain.

Amygdala

Part of temporal lobe...Learning fear, plays role in anxiety and aggression.

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Brain nucleus;

Collection of neuronal cell bodies inside the CNS, not including cortical gray of cerebral and cerebellar cortices

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Brain stem;

Collective term for medulla oblongata, pons and midbrain.

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Brain ventricles (4);

Lateral Ventricle largest of 4 ventricles in the brain. There are left and right lateral ventricles. Third and Fourth Ventricles are associated with the thalamus/hypothalamus and brain stem. All ventricles contain cerebrospinal fluid (CSF).

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Cerebral Aqueduct ;

Connects 3rd and 4th ventricles and also contains CSF.

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Cerebellum;

Cerebrum;

Divided into two cerebral hemispheres, each containing four major lobes (i.e., frontal, parietal, temporal and occipital). Also contains other major brain regions including the thalamus and hypothalamus.

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Corpus callosum;

Largest commissure in the brain (i.e., a commissure is white matter connection between both cerebral hemispheres); therefore, it connects the left and right cerebral hemispheres.

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Cranial nerves;

There are 12 pairs of cranial nerves. They are an extremely important part of the peripheral nervous system and connect directly to the brain . (Spinal nerves [see below] connect directly to the spinal cord.) Knowledge of cranial nerve connections and function essential in neurological diagnosis.

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Dorsal, lateral ventral columns of spinal cord;

These are the white matter of the spinal cord. They contain bundles of myelinated axons that carry information up and down the spinal cord. For example, the dorsal columns convey sensory information (e.g., touch) up the spinal cord to the brain. Lateral columns convey motor information from the brain down the spinal cord, as well as pain and temperature info up the spinal cord to the brain.

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Dorsal root ganglion;

Part of the peripheral nervous system, located adjacent spinal cord, one for each spinal nerve, contains cell bodies of vast majority of sensory neurons .

Frontal lobe(s) –

Ganglion;

Collection of neuronal cell bodies located outside of the central nervous system.

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Gray and white matter of brain and spinal cord;

Gray matter appears “gray” because contains high density of neuronal cell bodies, located in the CNS.White matter appears “white” because contains high density of myelinated axons , located in the CNS.

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Gyri(us);

Ridges and bumps of the cerebrum.

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Hippocampus;

Part of temporal lobe, for memory consolidation, spatial navigation, plays role in emotions. Damaged in Alzheimer’s.

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Hypothalamus;

Controls appetitive behaviors and much of endocrine system. Also plays major role in emotions.

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Longitudinal fissure;

Divides right and left cerebral hemispheres of the cerebrum.

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Massa intermedia (intermediate mass of thalamus);

Seen in mid sagittal view of thalamus.

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Medulla oblongata;

Most posterior part of the brain (hind brain). Contains many cranial nerve nuclei, tracts (i.e., collections of axons) from sensory and motor neurons, vestibular and auditory centers, cardiac center, and inspiratory center (breathing)

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Midbrain;

It does not include the thalamus or hypothalamus , as is often and mistakenly suggested in lay publications. Specifically located behind the hypothalamus and anterior to the pons. Contains the substantia nigra, some cranial nerve nuclei and .important motor and sensory tracts.

Occipital lobe(s) –

(1 of 4 major lobes of each cerebral hemisphere); Contains primary visual cortex.Note: Each main cerebral hemisphere lobe has primary regions and association areas which provide more complex information regarding each main function

Pineal gland/body ;

“3rd eye”. Descartes’ seat of the soul. Makes melatonin for circadian rhythms . Will be discussed further with endocrine system.

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Postcentral gyri(us);

Primary sensory cortex , located in parietal lobes.

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Pons;

Means bridge. Part of the brain stem. Contains sensory and motor tracts going up and down spinal cord, cranial nerve nuclei, and tracts interconnecting cerebellum with rest of the brain and spinal cord.

Sensory neurons;

Simple reflex arch (e.g., monosynaptic reflex);

Sensory neurons synapses with a lower motor neuron in the spinal cord. For example, stretch of patellar tendon is detected by a sensory neuron. The signal travels to the spinal cord where the sensory neuron synapses with a lower motor neuron that stimulates contraction of the quadriceps femoris

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Sulci(us);

Shallow groves between gyri.

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Spinal nerves;

31 pairs, part of peripheral nervous system. Are mixed, i.e., they contain axons from motor and sensory neurons.

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Superior & inferior colliculi(us);

together they comprise the corpora quadrigemina and roof of the midbrain. Involved in complex visual reflexes: Superior causes us to turn head when we see something in periphery. Inferior links auditory input to visual reflexes